Thermochemical characterization of biochar from cocoa pod husk prepared at low pyrolysis temperature

In this work, cocoa pod husk (CPH), a processing by-product from the cocoa industry, was evaluated as a potential feedstock for preparing biochar fuel at relatively low pyrolysis temperature. First, its thermochemical characteristics, including the calorific value and mineral component analyses, were investigated, showing that the bioresource obviously contained a large percentage of volatile matter. It thus had a higher heating value of 17.8 MJ/kg but showed a higher potassium content in ash (i.e., 4.03 wt%). A series of CPH-based biochars (i.e., CPHBC) were produced at different temperatures (i.e., 190, 220, 250, 280, 310, 340, and 370 °C) and residence times (i.e., 30, 60, 90, and 120 min). The resulting biochars were subject to the analyses of chemical and thermal properties. The calorific value of resulting biochar indicated an increasing trend with pyrolysis temperature, but there was slightly decreasing change at the longer residence time under the fixed pyrolysis temperature (i.e., 370 °C). The optimal biochar product had a thermochemical characteristics with high carbon (>60 wt%) and calorific value (>25 MJ/kg, dry basis). Furthermore, the CPH-based biochar showed a lignite-like feature based on the O/C and H/C molar ratios, but it would not be appropriate to be fired in boilers because of its high mineral contents (i.e., potassium).